considering the statement :
When adding an RDS instance to VPC, there needs to be three subnets in
the subnet group across three different AZs for that VPC
what is the difference between three subnets and AZs here?
I know that we need AZs for any RDS instance and it is created automatically by amazon at deployment time. So, this of course means that there should be one subnet in each three AZs to enable access to RDS replicas and instances. Or it means that each AZ should have three subnets created within to enable that?
Amazon provides 99.95% RDS availability
Multi-AZ configurations for MySQL, MariaDB, Oracle, and PostgreSQL are covered by the Amazon RDS Service Level Agreement ("SLA"). The RDS SLA affirms that AWS will use commercially reasonable efforts to make Multi-AZ instances of Amazon RDS available with a Monthly Uptime Percentage of at least 99.95% during any monthly billing cycle.
In order to achieve that database has to be replicated in three different AZ. That is the reason why Amazon requires three subnets in three AZ. The relationship is:
The region has more than one AZ
AZ belongs only to one region
AZ has more than one data center
AZ can have more than one subnets. However, there is a soft limit of 200 subnets per AZ. You can ask Amazon for more than 200 if you need.
Subnet belongs only to one AZ
VPC belongs only to one region. You can have more than one VPC per region. However, there is a soft limit of 5 VPCs per region. You can ask Amazon for more than 5 if you need.
VPC can span more than one AZ.
You can have as many Subnets as you like in each AZ. By default AWS creates one VPC containing one Subnet in each AZ. The number of AZ varies from region to region.
The quote you gave in your question is saying that you must have three subnets, that these three subnets must all be be in different AZ but all three subnets must be in the same VPC.
Related
As part of our project we are using AWS RDS postgres service. While creating RDS service AWS mandated to create two subnets from different AZs (ex: us-west-2a and us-west-2b). But we have only one subnet. Is there any way to overcome this problem.
Thanks in advance.
To ensure High Availability, you need to specify subnets in two different Availability Zones (AZs).
Each AZ operates in a different data center. If an AZ fails, the Amazon RDS service will automatically launch a replacement database in a different AZ. Therefore, it requires a minimum of two different AZs to be specfiied.
For Subnets in the same VPC, is Region independent?
I would like to set up more than two fully independent Availability Zones for Elastic Load Balancer(ELB).
Is it possible?
Yes:
Within a Region you create a VPC
The VPC is a logical concept and spans AZs
You then create subnets within the VPC for each AZ
Each AZ is a physically separate datacentre from another, normally 3 AZs or more per region
When you set up an ELB, you select the subnets that you want to use, select a subnet in each AZ
ELB will add instances across all 3 (or more) subnets/AZs
I'm trying to create an Aurora DB instance using a CloudFormation script. It requires me to have subnets with 2 availability zones. I entered 2 subnets which have different AZs, but now I get this error in the stack creation log:
DatabaseSubnetGroup: Subnet has different VPC Id: vpc-dd3bf9ba than vpc-e0e11ab7.
What does this error mean?
It sounds like the two subnets, although in different availability zones (AZs) are part of two separate VPCs (logical network isolation). You would need to select two subnets in different AZs but in the same VPC.
I have configured an AWS auto-scale group with 2 available zones: us-east-1a and us-east-1c . Today, with the issue AWS had on us-east-1a, I noticed that new instances are not created on us-east-1c zone.
Any clues on what I should check on?
Thank you.
Amazon EC2 Auto Scaling can deploy EC2 instances across multiple Availability Zones within one region.
It cannot deploy instances across multiple Availability Zones.
If you wish to implement redundancy across regions, you would need to configure Amazon Route 53 with a health check to route traffic to instances or load balancers in different regions. However, Auto Scaling would continue to operate independently in each region.
1, if 2 EC2 instances in separated VPC in the same AZ, so they can not connected by private IP right? so BOTH of ec2 will be charged the regional data transfer fee right?
2, said 2 ec2 instances in the same AZ from 2 separated AWS accounts. It is very common case due to lot of servers are from EC2. For example, one ec2 instance is from a 3rd party service provider, and one instance is from me. Even if they are in the same AZ, When my ec2 send/receive data from/to that ec2 from 3rd party, BOTH of us will be charged regional data transfer fee, right?
3, Is it possible to use private IPs to connect/send traffic between EC2 instances in the same AZ from different accounts?
4, how can I launch a ec2 without VPC?
VPCs can be peered, in which case the instances can communicate via private IP addresses, as long as the CIDR supernets of the VPCs don't overlap.
However, you'll still be charged the regional transfer rate.
There is no such concept as instances from two different AWS accounts being in "the same" availability zone, because this isn't something you can readily determine, and even if you can, it doesn't matter:
To ensure that resources are distributed across the Availability Zones for a region, we independently map Availability Zones to identifiers for each account. For example, your Availability Zone us-east-1a might not be the same location as us-east-1a for another account. Note that there's no way for you to coordinate Availability Zones between accounts.
—http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-regions-availability-zones.html
The charge is always the same, between accounts -- it's regional data transfer, within the region.
Note that both instances are billed $0.01/GB. The net charge, then, is $0.02/GB, split across the two instances, whether you use private or public IP addresses, the charge is the same whether you use VPC peering or simple connect directly over public IP addresses.